Recently, ink-jet recording systems have been applied in various fields of printing such as printing on photographs, various type of prints, marking, and color filters since images can be formed simply at a low price by ink-jet technology. Image quality comparable to pictures by silver salt photography can be obtained by using image recording apparatuses capable of ejecting and controlling fine dots of ink, inks exhibiting an improved color reproducing range, image durability and ink ejection suitability, as well as exclusive paper considerably improved in ink absorbability, color appearance of the coloring material and image surface glossiness. The improved image quality of current ink-jet recording systems has been attained only by combination of the recording apparatus, ink and exclusive paper.
However, ink-jet systems requiring exclusive paper poses problems such as restrictions of such paper and cost of the recording media. Consequently, various trials for recording an image on recording media other than exclusive paper have been carried out. Specifically, such methods include a phase changing ink-jet system using a wax based ink which is solid at room temperature, a solvent type ink-jet system using an ink principally composed of a quick drying organic solvent and a UV ink-jet system using an ink curable by ultraviolet rays (being UV light).
Among these, the UV ink-jet system has recently become popular because due to its relatively reduced odor than the solvent type ink-jet system, and capable of printing on recording media which lack the ability of quick drying and ink absorbability, as well as UV curable ink-jet inks have been disclosed, cf. Patent Documents 1-5, for example.
As the coloring material, pigment dispersion is frequently used from the viewpoint of color fastness. A polar group derived from a polymerizable group is incorporated in the active ray curable ink-jet ink even though the ink employs solvent. However, the pigment does not readily adsorb the dispersing agent in such a system. Dispersion of the pigment is a more important problem in the ink-jet ink compared to the typical paints. When the dispersion is not uniform, ejection of the ink becomes unstable and a major problem when using ink-jet ink.
It is widely known that pigment in usual active ray curable ink can be dispersed using a basic dispersing agent. However, stable dispersion could not be obtained during the testing by the inventors. Further, limitations due to the number of coarse particle is disclosed, for example, in Patent Documents 6 and 7, but stable ejection even with such limitation, cannot be attained of non-aqueous active ray curable ink. As a result, high definition images cannot be recorded at high reproducibility and high production stability.
Patent Document 1: Unexamined Japanese Patent Application Publication No. (hereinafter, referred to as JP-A) 6-200204 (Claims and Examples)
Patent Document 2: JP-A 2000-504778 (Claims and Examples)
Patent Document 3: JP-A 2002-188025 (Claims and Examples)
Patent Document 4: JP-A 2002-60463 (Claims and Examples)
Patent Document 5: JP-A 2003-252979 (Claims and Examples)
Patent Document 6: JP-A 11-140356 (Claims and Examples)
Patent Document 7: JP-A 2000-204305 (Claims and Examples)